6-2-5-predicting-inheritance-dihybrid-crosses

课 Progress

0% Complete

Predicting Inheritance: Dihybrid Crosses

Monohybrid crosses look at how the alleles of one gene transfer across generations
Dihybrid crosses look at how the alleles of two genes transfer across generations
- I.e. dihybrid crosses can be used to show the inheritance of two different characteristics in an individual
The genetic diagrams for both types of crosses are very similar
For dihybrid crosses, there are several more genotypes and phenotypes involved
When writing out the different genotypes, write the two alleles for one gene, followed immediately by the two alleles for the other gene. Do not mix up the alleles from the different genes
- For example, if there was a gene with alleles Y and y and another gene with alleles G and g an example genotype for an individual would be YyGg

Horses have a single gene for coat colour that has two alleles:
- B, a dominant allele produces a black coat
- b, a recessive allele produces a chestnut coat
Horses also have single gene for eye colour
- E, a dominant allele produces brown eyes
- e, a recessive allele produces blue eyes
Each of these genes (consisting of a pair of alleles) are inherited independently of one another because the two genes are located on different non-homologous chromosomes
- Such characteristics are said to be unlinked
In this example, a horse that is heterozygous for both genes has been crossed with a horse that is homozygous for one gene and heterozygous for the other

Parental phenotypes: black coat, brown eyes x chestnut coat, brown eyes

Parental genotypes: BbEe bbEe

Parental gametes: BE or Be or bE or be bE or be

Dihybrid Cross Punnett Square Table

Predicted ratio of phenotypes in offspring = 3 black coat, brown eyes : 3 chestnut coat, brown eyes : 1 black coat, blue eyes : 1 chestnut coat, blue eyes
Predicted ratio of genotypes in offspring = 3 BbEE : 3 bbEE : 1 Bbee : 1 bbee